1. Field of the Invention
The present invention relates to a semiconductor device having a buffer layer that is used to prevent diffusion of copper atoms into a main body.
2. Description of the Related Art
Currently, in the field of manufacturing an integrated circuit having electrical components, such as high electron mobility transistors, gold (Au) and aluminum (Al), both of which have good electrical conductivity, are used as main materials for an electrode structure to electrically connect the respective electrical components in the integrated circuit. Although gold has excellent electrical conductivity and thermal conductivity, it is relatively rare as compared with other metals, such as aluminum, and thus, is relatively expensive. Therefore, in order to minimize the manufacturing cost of the integrated circuit, the amount of gold used for producing the integrated circuit has to be reduced. On the other hand, although aluminum is relatively inexpensive, its electrical conductivity and thermal conductivity are relatively poor compared to gold. Thus, when aluminum is used in an integrated circuit with minimized size, over-heating and high power consumption might occur, thereby resulting in premature degradation of the integrated circuit and insufficient battery endurance.
It is known that copper has high electrical conductivity and good thermal conductivity, and is relatively inexpensive. Thus, it is suitable for use as a main material for an electrode. Therefore, in the field of integrated circuits that use high electron mobility transistors as the main electrical components, introduction of a copper plating process is required for further development.
Referring to FIG. 1, a conventional semiconductor device, e.g., a high electron mobility transistor, includes a substrate 111, a main body 11, a gate structure 12, and two electrode structures 13.
The main body 11 is formed on the substrate 111, and includes a first film layer 112 that is mainly made of gallium nitride, and a second film layer 113 that is mainly made of aluminum gallium nitride.
The gate structure 12 is formed on an upper surface of the second film layer 113 of the main body 11 that is opposite to the first film layer 112, and is made of a conductive material, e.g., a metal.
The electrode structures 13 are formed on the upper surface of the second film layer 113 and are spaced apart from the gate structure 12, and include an ohmic contact layer 131 and a circuit layer 132. The ohmic contact layer 131 is made of an alloy consisting essentially of titanium, aluminum, and nickel. The circuit layer 132 is mainly made of copper and is adapted to be welded with wires so as to electrically connect to an external circuit.
The channel is formed in the top of the second film layer 113 in the main body 11. One of the electrode structures 13 serves as a drain, and the other one of the electrode structures 13 serves as a source. Further, the gate structure 12 serves as a gate.
Under an ideal state, when a voltage is applied to the gate and the drain from the external circuit through the wires, voltage differences are formed between the gate and the main body 11 and between the drain and the source. At this time, a current may flow from the drain to the source through the channel so that the semiconductor device may be actuated.
However, because copper has great activity, when the electrode structures 13 of the semiconductor device are manufactured and/or are actuated, the copper atoms of the circuit layer 132 are liable to pass through the ohmic contact layer 131 and diffuse into the second film layer 113 and even the first film layer 112 of the main body 11, thereby resulting in poor electrical properties and inferior reliability of the semiconductor device.